Hi all,

I'm getting a bit stressed about this haha, I can't get the rear brake lines to bleed, no pressure builds up, no matter how much I pump the brakes.

I bled the front before the rear by mistake, which was fine, but this may have caused the problem? Maybe the pressure differential is causing some sort of issue?

I dropped into a Jag workshop and talked to a (disinterested) jag repair man, he said that the master cylinder has separate ?cylinders? that pressurize both the front and the rear brakes. Maybe I broke the rear one while I was bleeding the front brakes?

What do we think? I really want to get this car back on the road or its going to rot away into nothing!

Harry

 

How I would approach it....

Disconnect the rear circuit and air check it. lift the rear wheels off the ground so you can turn them by hand. Use compressed air to check the operation of the rear brakes. A stiff peice of 1/4 fuel line clamped to the line and the other side to a compressed air source with about 30 to 40 psi. That should tell you if the rear brakes work and hold pressure becasue you should not be able to turn the wheels by hand with even minimal pressure.

If the rear brakes work, then I'd replace the MC and bleed the whole system.

If they dont pass then remove the rear cage, install new calipers and blow out the lines. Then install a new MC and bleed.

Easy for me to say.

 

What's the history here?

Were the brakes working recently?

Have you replaced some parts? Just flushing out old fluid?

When you bled the fronts did you push the pedal *all the way down*? if so, that can cause a problem in some cases because the m/c pistons are then moving in cruddy, corroded, disreputable territory where they don't normally go....damaging the seals.

Doing the fronts first wouldn't cause any damage that I can think of.

Are you sure your bleeding method/equipment isn't allowing air to be sucked back in?

I've found that the brakes on these older Jags bleed quite easily....but that doesn't mean a stubborn case can't come along. Lord knows I've come across a few cars that seem to defy me for hours. The next one might bleed in 15 minutes as I whistle away.

Sometimes, if faced with a belligerent system, I just top off the m/c, open a bleeder, and walk away for a few hours...letting gravity push the air bubble out. Sometimes it works, sometimes not.

Cheers
DD

 

My 2 cents:
I would check the proportioning valve. Remove the main line going to the valve and with a small pick you could recenter the valve position. Had this happen to me once but it was on a GM vehicle. I do not know it applies to your Jaguar.

 

Always unnerves me when I read about backyard mechanics trying to solve brake related problems. I really feel that if you do not understand how your car's braking system works - take it to a brake shop.
I realize this is an enthusiasts site but sometimes car owners underestimate the task at hand and overestimate their skills.
You may not agree... but if one of your family gets severely injured or worse, because they were involved in a car accident, where the cause of the accident was attributed to defective brakes, you may want to reconsider. Why were the brakes considered "defective" ?

Can not be too careful when working on brakes...work on anything else and it fails - they car will most likely stop, if the brakes fail it will not stop.

Yes I do work on my own brakes on my Jag and my Astro van, But I have been working on my own vehicles for over 50 years. Both my van and the Jag are old technology (no traction control or ABS ) and I understand them,. having owned them for several years. If you were to ask me to work on the brakes on your 2018 Booboo mobile,. I will pass -"take it to a brake shop" just an opinion..

 

Yeah, brakes gotta be right. In my early days, I got away with driving cars that had lousy brakes. A different era!!!


Decades ago, I went to a brake shop to buy a couple of "hardware kits" for an older car. The tech grudgingly sold them to me, but asked me to bring the finished car over and they would check it gratis! I did ! I passed muster.


Carl

 

Hi all, Thanks for all the replies, bear with me as I work through each one.

Got all new calipers front and rear, hoses actually, I think it might not be a bad idea to replace the MC anyway its old and the seals were leaking on the connection to the fluid tank.

I do worry about those old brake lines, is there an effective way of replacing them? Other than bending your own?

Thanks for the tips, Ill see what I can do.

Heya Doug,
All the calipers and pads are new in the last 5000km.

The original task was to replace the seals on the top of the master cylinder.
Which lead me to get a bit excited and disconnect the brake lines, and thus no pressure in the system.

I now think that if the seals on the top of the cylinder went bad, then the ones on the inside are likely to have gone bad too.

Bleeding method and kit should be good, I've bled them multiple times with no issues.

I was thinking this too, as I have read in the Haynes manual that this could get biased to one side and cause similar problems, Ill try the method in the Haynes manual for resetting,which I believe is what you are suggesting.

Don't worry, I'll be going right off to the brake man to get them bled professionally once I have some pressure in the system to get around the corner, mechanic is about 2 minutes away luckily. The brakes weren't really faulty, just leaking a bit of fluid from the tank, Ill go slow, there's very little traffic out here.

 

Probably just too much air right now. Try gravity bleeding the rear and go from there. Google a video on dual servo master cylinders to gain a little bit of understanding on how most modern braking systems work.

 

Have you run over anything lately, i had that happen once and i had run over a crooked manhole cover, and after much deliberation foundnthatbthe cover had popped up and totally crushed my brake line going to rear, basically i was driving around for at least a few weeks just on front brakes!!!! Didnt onow until one day i had to do an emergency stop, well that created enough pressure to get fluid past the crushed spot! I stopped ( luckily) but damn sure couldnt go again afterwards, fluid could not escape and brakes were locked on!!

 

So they bled, and there's good pressure.

However, there's always a problem with these cars haha, the brake booster has given up the ghost in the process.

I get a nice hissing sound while I push the brake pedal and push all the air out, then the pedal gets hard and the brakes kick in when I finally make contact with the master cylinder which stops me just fine, well, good enough to get to the mechanic.

So, I'll need to replace the brake booster.

Any tips?

I'll get the master cylinder reconditioned at the same time I guess. I have a set of seals I can give the rebuild shop.


OK so this and a change of technique is what got the rears to bleed.

I left the bleeders open for a day and then tried again and got some fluid through.

(What follows can be read in many ways...)

Normally I have only ever done the "Tighten, pump pump pump, release pressure, hold, tighten, pump..." technique, where as this time we started with just a bunch of pumping until the fluid was flowing well, followed by the above technique.

Whoa, that's not ideal! I'm not completely sure to be honest, but I've found the problem I think.

However, you might be able to answer this question:

If I was to want to replace any brake lines, how should I go about that?
Bend my own? Or buy a set? I haven't seen any new ones for this car online ever, but who knows.

I know I have a brake line with a slight crush in it that leads to my front left caliper and they are rusty and old on the outside, which makes me want to replace them.

Harry

 

Try Classic Tube:
Prebent Tubing Automotive
They list Jaguar among their models. Sometimes they even have stainless.
(';')

 

Cupro-nickel pipe is normally best (aka "kunifer" - copper, nickel, and a very small bit of iron). Pure copper can suffer fatigue fractures. It is also possible to buy a bending tool for the 3/16 piping.

 

The symptom you described is a air in the system, not a bad booster. The symptoms for the booster would be leaking fluid around the booster and no assistance when pressing the pedal (like using the brakes with the engine off).

If you have to press the pedal to the floor to get brakes, its because most of the pedal travel is compressing air instead of applying hydraulic force through the system. My mistake if I misunderstood your post, but if that is the only symptom, I wouldn't go replacing the booster. If you want to test it, pull the hose leading to it and see if it will hold a vacuum.